Room-temperature NIR phosphorescence of new iridium (III) complexes with ligands derived from benzoquinoxaline

Abstract

A new series of new iridium (III) complexes (1–5) bearing ligands derived from benzoquinoxaline were designed and synthesized. X-ray structural analyses of 1 reveal a distorted octahedral geometry around the Ir atom in which the pyrazolate chelate is located opposite to the cis-oriented carbon donor atoms of benzoquinoxaline, while the benzoquinoxaline ligands adopt an eclipse configuration and their coordinated nitrogen atoms and carbon adopt trans- and cis-orientation, respectively. Complexes 1–5 exhibit moderate NIR phosphorescence with peak maxima located at around 910–930 nm. As supported by the TDDFT approach, the transition mainly involves benzoquinoxaline 3π–π* intraligand charge transfer (ILCT) and metal (Ir) to benzoquinoxaline charge transfer (MLCT) of which the spectroscopy and dynamics of relaxation have been thoroughly investigated. The relatively weak NIR emission can be tentatively rationalized by the low energy gap of which the radiationless deactivation may be governed by nearly temperature-independent, weak-bonding motions in combination with a minor channel incorporating small torsional motions associated with phenyl ring in the benzoquinoxaline sites.Key words: phosphorescence, NIR, iridium, benzoquinoxaline, isoquinoline, bipyridine, pyrazolate, acetylacetonate.

Boosting Efficiency of Near‐Infrared Emitting Iridium(III) Phosphors by Administrating Their π–π Conjugation Effect of Core–Shell Structure in Solution‐Processed OLEDs

“…It is obvious that the iridium complexes of Ir1 and Ir3 with the shells anchored at 3, 6‐positions exhibit better EL performance than their isomers of Ir2 and Ir4 with the shells anchored at 11, 12‐positions. In comparison with the previous reports, [ 17,18,29 ] the presented iridium complexes of Ir1 and Ir3 exhibit more outstanding EL performances. Although the EQE levels tend to decrease with increasing doping concentrations, the efficiency roll‐off is efficient controlled at high current densities in these devices.…”

Cationic IrIII Emitters with Near‐Infrared Emission Beyond 800 nm and Their Use in Light‐Emitting Electrochemical Cells

“…The molecular design of the guest ionic iridium complexes was based on the incorporation of electron‐donating groups into the C^N ligands and the introduction of electron‐withdrawing groups into the N^N bidentate ligand to generate a smaller energy gap. In addition, the π‐conjugated system was extended to reduce the gap, leading to NIR emission . As shown in Scheme , the 2,3‐diphenylbenzo[ g ]quinoxaline derivatives mpqx or mopqx were synthesized by the reaction of commercially available 2,3‐naphthalenediamine and substituted benzil in the presence of iodine as catalyst for the condensation reaction.…”

Synthesis, photophysical, electrochemical and electroluminescence studies of red emitting phosphorescent Ir(III) heteroleptic complexes

“…1 H and 13 C NMR spectra were recorded using Bruker spectrometer with working frequency 500 MHz for 1 H NMR and 125 MHz for 13 C NMR. For 1 H NMR and 13 C NMR, the chemical shifts were referenced to CH 2 Cl 2 or CHCl 3 present as an impurity in the deuterated solvent. Mass spectra were measured using a Thermo Finnigan LCQ Deca Electrospray quadrupole ion trap mass spectrometer (Thermo Electron Co., Hemel Hempstead, Herts, UK) or on MALDI-TOF (Micromass Tof Spec 2E).…”

“…The optical spectra of Ir complexes have been studied experimentally and theoretically. [11][12][13][14][15][16] The absorption spectra in the UV-Visible region consist singlet and triplet transitions of the type π −π * and MLCT. The normally forbidden triplet transition is strongly allowed to such an extent that the extinction coefficients of 3 π − π * and 3 MLCT are comparable to the corresponding singlet transitions in some complexes.…”

“…10 The emission colour of an Ir Complex is tuneable in different ways like changing C ∧ N ligand structure in a homoleptic complex and by changing ancillary ligand in a hetroleptic complex. [11][12][13][14] A number of studies have revealed a wealth of information on the photophysical, electrochemical, and electroluminescence properties of a large number of Ir complexes, apart from valuable information on synthetic routes and theoretical studies on these molecules. [15][16][17] Among the many cyclometalating ligands, it is shown that Ir complex of 1-phenyl isoquinoline (piq) has superior performance in electroluminescence.…”